You should really use non setting mastic as Tiger seal is a serious adhesive and will stick every thing up, to the degree you will destroy the metal seal retainers as they are very flimsy, should you need to remove them, which you would need to do if you replace the roof (you will just make hard work for yourself in the long run). This will not neccesarily cure a porous roof and the water will find another entry point. By all means change the foam gasket seals with new ones Part No 155871431 from VW dealer, their main job is to keep out the draft, moisture, noise etc.
If the roof is old and has any damage just replace it. It's not that difficult, just time consuming and you need a bit of patience.
When the roof goes porous the moisture seeps through the Vynil/mohair and runs towards the natural curve to the outer edges, it collects in the roof frame arm sections. The water finds it's way in usually around the roof latch handle area, but will find an easy entry point and so drips in.
I would replace the foam gasket seals and make sure the front section of the seals make contact with the main header seal.
